Water-based ink for ink-jet recording, ink cartridge, ink-jet recording apparatus, and ink-jet recording method

ABSTRACT

There is provided a water-based ink for inkjet recording, including: a self-dispersible pigment modified by carboxylic acid group; glycerol; diethylene glycol; alkylene glycol monoalkyl ether; and water, wherein the glycerol and the diethylene glycol satisfy the following condition (i):
 
0.24≦DEG/(Gly+DEG)≦0.92  (i)
 
in the condition (i), Gly represents an amount of the glycerol in the water-based ink (% by weight); and DEG represents an amount of the diethylene glycol in the water-based ink (% by weight).

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent ApplicationNo. 2012-251525, filed on Nov. 15, 2012, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a water-based ink for inkjet recording,an ink cartridge, an ink jet recording apparatus, and an ink jetrecording method.

2. Description of the Related Art

It is important for a water-based ink for inkjet recording to suppressviscosity increase and solidification due to drying in order todischarge the water-based ink stably. Thus, a humectant (antidryingagent) is generally used in the water-based ink for ink jet recording.There have been suggested, for example, a water-based ink for ink jetrecording in which glycerol is used as the humectant (Japanese PatentApplication laid-open No. 2011-225759) and a water-based ink for ink jetrecording in which diethylene glycol is used as the humectant (JapanesePatent Application laid-open No. 2006-96990 corresponding to UnitedStates Patent Application Publication No. 2006/0146108).

However, the water-based ink for ink jet recording in which thediethylene glycol is used has the following problem. That is, althoughthe diethylene glycol has a low viscosity, the diethylene glycol isrelatively high-volatile compared with other humectants. Thus, thediethylene glycol is volatized due to drying. Therefore, the water-basedink for ink jet recording in which the diethylene glycol is used can notobtain the viscosity-increase suppressing effect after the dryingsufficiently. For the water-based ink for ink jet recording in which theglycerol is used, since the volatility of glycerol is lower than that ofdiethylene glycol, solidification is suppressed by the glycerol evenwhen moisture or water content is lost due to the drying. However, theviscosity of glycerol is relatively high, and thus theviscosity-increase suppressing effect after the drying is not enough. Asdescribed above, both the water-based ink for inkjet recording in whichthe glycerol is used and the water-based ink for ink-jet recording inwhich the diethylene glycol is used have the insufficientviscosity-increase suppressing effects after the drying. Thus, thewater-based ink for inkjet recording in which the glycerol or thediethylene glycol is used is required to further suppress the viscosityincrease after the drying. In order to stably discharge the water-basedink by suppressing the viscosity increase after the drying, it isnecessary that both jetting stability after an ink jet recordingapparatus is not used and is left for a short period of time (forexample, a few seconds to several tens of seconds) (short-term drying)and jetting stability after the ink jet recording apparatus is not usedand is left for a long period of time (for example, a month to a fewmonths) (long-term drying) are superior. In addition, it is necessarythat a re-dispersion property, which is an aspect of the jettingstability after the long-term drying, is superior.

SUMMARY OF THE INVENTION

In view of the above, an object of the present teaching is to provide awater-based ink for ink jet recording in which viscosity increases aftera short-term drying and a long-term drying are suppressed and are-dispersion property is superior.

According to a first aspect of the present teaching, there is provided awater-based ink for ink-jet recording, including a self-dispersiblepigment modified by carboxylic acid group, glycerol, diethylene glycol,alkylene glycol monoalkyl ether, and water, wherein the glycerol and thediethylene glycol satisfy the following condition (i):0.24≦DEG/(Gly+DEG)≦0.92  (i)in the condition (i), Gly represents an amount of the glycerol in thewater-based ink (% by weight); and DEG represents an amount of thediethylene glycol in the water-based ink (% by weight).

According to a second aspect of the present teaching, there is providedan ink cartridge containing the water-based ink for ink-jet recording asdefined in the first aspect.

According to a third aspect of the present teaching, there is providedan ink jet recording apparatus including: an ink accommodating sectionin which the water-based ink for ink jet recording as defined in thefirst aspect is accommodated; and an ink discharge mechanism which isconfigured to discharge the water-based ink for ink jet recordingaccommodated in the ink accommodating section.

According to a fourth aspect of the present teaching, there is providedan ink jet recording method including: preparing a recording medium; anddischarging the water-based ink for ink jet recording as defined in thefirst aspect onto the recording medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view showing an example of a structureof an ink jet recording apparatus of the present teaching.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The degree of viscosity increase of the water-based ink after ashort-term drying and the degree of viscosity increase of thewater-based ink after a long-term drying can be evaluated, for example,by using viscosity of the water-based ink after evaporation in a lowshear area and viscosity of the water-based ink after evaporation in ahigh shear area as indexes. The viscosity of the water-based ink afterthe evaporation in the low shear area is used as an index of performancerequired when the water-based ink is redischarged from an ink dischargemechanism of an ink jet recording apparatus after the long-term drying.As the viscosity of the water-based ink after the evaporation in the lowshear area is lower, the viscosity increase of the water-based ink afterthe long-term drying is further suppressed, and thereby making itpossible to provide a superior jetting stability after the long-termdrying. The viscosity of the water-based ink after the evaporation inthe high shear area is used as an index of performance required when thewater-based ink is redischarged from the ink discharge mechanism of theink jet recording apparatus after the short-term drying. As theviscosity of the water-based ink after the evaporation in the high sheararea is lower, the viscosity increase of the water-based ink after theshort-term drying is further suppressed, and thereby making it possibleto provide a superior jetting stability after the short-term drying. Theviscosity of the water-based ink after the evaporation in each of thelow shear area and the high shear area can be measured, for example, bya method explained in Examples which will be described later. The lowshear area means, for example, an area in which a shear velocity is notmore than 10 sec⁻¹ (more specifically 1 sec⁻¹ to 10 sec⁻¹). By measuringthe viscosity in the low shear area, viscosity corresponding to theviscosity after the long-term drying can be evaluated. The high sheararea means, for example, an area in which the shear velocity is not lessthan 100 sec⁻¹ (more specifically 100 sec⁻¹ to 1000 sec⁻¹). By measuringthe viscosity in the high shear area, viscosity corresponding to theviscosity after the short-term drying can be evaluated.

The re-dispersion property of the water-based ink in the presentteaching means, for example, solubility and dispersion property of asolid matter, in a water-based ink, generated after the water-based inkis once evaporated to dryness with resultant solid matter, thesolubility and dispersion property being those of when the solid matteris then newly brought in contact with the water-based ink. There-dispersion property of the water-based ink can be measured, forexample, by a method explained in Examples which will be describedlater.

An explanation will be made about the water-based ink of the presentteaching. The water-based ink of the present teaching includes acolorant, water, a humectant, and a penetrant.

The colorant includes a self-dispersible pigment modified by carboxylicacid group (hereinafter referred to as “carboxylic acid group-modifiedself-dispersible pigment”). As the carboxylic acid group-modifiedself-dispersible pigment, it is possible, for example, to use acommercially available product. The commercially available productincludes, for example, “CAB-O-JET (trade name) 300” produced by CabotSpecialty Chemicals. The water-based ink may contain any polymericpigment dispersant; or it is allowable that the water-based ink does notcontain any polymeric pigment dispersant. In a case that the water-basedink contains the polymeric pigment dispersant, it is preferable that thepolymeric pigment dispersant is contained in the water-based ink in anamount to an extent not affecting the viscosity of the water-based ink.As described above, since the carboxylic acid group-modifiedself-dispersible pigment is used in the water-based ink of the presentteaching, the problem of viscosity increase due to the polymeric pigmentdispersant does not occur, and the jetting stability and storagestability are superior.

The solid content blending amount of the carboxylic acid group-modifiedself-dispersible pigment (pigment solid content) with respect to theentire amount of the water-based ink is not particularly limited, andmay be appropriately determined based on, for example, desired opticaldensity or color (hue, tint), etc. The pigment solid content is, forexample, 0.1% by weight to 20% by weight, is preferably 1% by weight to15% by weight, and is more preferably 2% by weight to 10% by weight.

The colorant may further contain any other pigment, dye, etc., inaddition to the carboxylic acid group-modified self-dispersible pigment;or it is allowable that the colorant does not contain any other pigment,dye, etc. In terms of improving weatherability or weather resistance ofa printed matter, it is preferable that the water-based ink of thepresent teaching does not contain the dye as the colorant. Further, itis preferable that the water-based ink of the present teaching containsonly the carboxylic acid group-modified self-dispersible pigment as thecolorant substantially. By using only the carboxylic acid group-modifiedself-dispersible pigment as the colorant, it is possible to furthersuppress the viscosity increase of the water-based ink after the dryingand to further improve the re-dispersion property. In a case that thecolorant contains any other pigment or dye other than the carboxylicacid group-modified self-dispersible pigment, the blending amount of anyother pigment or dye is preferably not more than 10% by weight withrespect to the entire amount of the colorant so as not to affect theeffect of the present teaching.

It is preferable that the water is ion exchange water or pure water(purified water). The blending amount of water (water ratio) withrespect to the entire amount of the water-based ink is, for example, 10%by weight to 90% by weight, and is preferably 40% by weight to 80% byweight. The water ratio may be, for example, the balance of the othercomponents.

The water-based ink contains glycerol and diethylene glycol as thehumectant. By using the glycerol and the diethylene glycol incombination as the humectant, the water-based ink of the presentteaching has such an advantage that properties of water retentionability of the glycerol and low-viscosity ability of the diethyleneglycol are provided effectively. By selecting the carboxylic acidgroup-modified self-dispersible pigment as the colorant and blending theglycerol and the diethylene glycol to satisfy the following condition(i), it is possible to obtain the water-based ink in which the viscosityincreases after the short-term drying and the long-term drying aresuppressed.0.24≦DEG/(Gly+DEG)≦0.92  (i)Gly: Blending amount of the glycerol with respect to the entire amountof the water-based ink (% by weight)DEG: Blending amount of the diethylene glycol with respect to the entireamount of the water-based ink (% by weight)

The total blending amount of the glycerol and the diethylene glycol withrespect to the entire amount of the water-based ink is, for example, 10%by weight to 60% by weight. By making the total blending amount of theglycerol and the diethylene glycol to be not less than 10% by weight,the viscosity of the water-based ink is lowered, wet or moist conditionis sufficient, the viscosity increase after the drying is prevented, andvolatilization of the water-based ink is suitably suppressed. Further,by making the total blending amount of the glycerol and the diethyleneglycol to be not more than 60% by weight, the viscosity increase of thewater-based ink is suitably suppressed and the jetting failure isprevented. The total blending amount of the glycerol and the diethyleneglycol is preferably 15% by weight to 50% by weight. The blending amountof the glycerol with respect to the entire amount of the water-based inkis, for example, 1% by weight to 45% by weight, preferably 1% by weightto 40% by weight, and more preferably 1% by weight to 30% by weight. Theblending amount of the diethylene glycol with respect to the entireamount of the water-based ink is, for example, 2% by weight to 55% byweight, preferably 3% by weight to 45% by weight, and more preferably 3%by weight to 35% by weight. The humectant may contain any humectantother than the glycerol and the diethylene glycol, but is preferablymade only of the glycerol and the diethylene glycol. For each of theglycerol and the diethylene glycol, a content rate of hydroxyl group tomolecular weight is high. Thus, the glycerol and the diethylene glycolare more likely to be solvated with component(s) of the pigment and thelike, and it is possible to suppress aggregation of the component(s) ofthe pigment and the like even after the drying. However, triethyleneglycol, dipropylene glycol, or the like does not provide the aggregationsuppressing effect, because the content rate of hydroxyl group tomolecular weight is low.

The glycerol and the diethylene glycol are preferably blended to meetthe following condition (ii) instead of the above condition (i). Bymeeting the following condition (ii), it is possible to obtain thewater-based ink in which the viscosity increases after the short-termdrying and the long-term drying are further suppressed.0.76≦DEG/(Gly+DEG)≦0.80  (ii)Gly: Blending amount of the glycerol with respect to the entire amountof the water-based ink (% by weight)DEG: Blending amount of the diethylene glycol with respect to the entireamount of the water-based ink (% by weight)

In a case that the carboxylic acid group-modified self-dispersiblepigment is used as the colorant and that the condition (i) or condition(ii) for the relation between the blending amount of glycerol and theblending amount of diethylene glycol is satisfied, the effect ofsuppressing the viscosity increase of the water-based ink after theshort-term drying and the viscosity increase of the water-based inkafter the long-term drying can be obtained. That is, in a case that thedye, a pigment which is not self-dispersible, a self-dispersible pigmentmodified by functional group other than carboxylic acid group, or thelike is used as the colorant, even when the condition (i) or condition(ii) is satisfied, the effect similar to that of the present teachingcan not be obtained. The reason there of is not clear, but it is assumedas follows. That is, it is considered that carboxylic acid ion of thepigment has interaction with hydroxyl group contained in the diethyleneglycol or hydroxyl group contained in the glycerol. This interaction isassumed to be mainly a hydrogen bond, and this interaction suppressesaggregation of the carboxylic acid group-modified self-dispersiblepigment after evaporation of volatile components in the water-based ink.As a result, it is possible to suppress the viscosity increase of thewater-based ink after the short-term drying and the viscosity increaseof the water-based ink after the long-term drying.

The humectant other than the glycerol and the diethylene glycoldescribed above is not specifically limited, which includes, forexample, lower alcohols such as methyl alcohol, ethyl alcohol, n-propylalcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, andtert-butyl alcohol; amides such as dimethylformamide anddimethylacetamide; ketones such as acetone; ketoalcohols (ketonealcohols) such as diacetone alcohol; ethers such as tetrahydrofuran anddioxane; Polyether such as polyalkylene glycol; polyhydric alcohols suchas alkylene glycol and trimethylolpropane; 2-pyrrolidone;N-methyl-2-pyrrolidone; and 1,3-dimethyl-2-imidazolidinone. Thepolyalkylene glycol includes, for example, polyethylene glycol andpolypropylene glycol. The alkylene glycol includes, for example,ethylene glycol, propylene glycol, butylene glycol, triethylene glycol,dipropylene glycol, tripropylene glycol, thiodiglycol, and hexyleneglycol. One type (kind) of the humectant as described above may be usedsingly, or two or more types (kinds) of the humectants as describedabove may be used in combination. Among them, it is preferable to usepolyhydric alcohol such as alkylene glycol.

The water-based ink contains alkylene glycol monoalkyl ether as thepenetrant. By containing the alkylene glycol monoalkyl ether in thewater-based ink, the water-based ink having a superior re-dispersionproperty can be obtained.

The alkylene glycol monoalkyl ether may be represented by the followinggeneral formula (1):R¹O—(R²O)_(n)—H  (1)In the general formula (1), R¹ is preferably an unsubstitutedstraight-chain alkyl group having 1 to 6 carbon atoms and is morepreferably an unsubstituted straight-chain alkyl group having 3 to 4carbon atoms; R² is preferably an unsubstituted straight-chain alkylenegroup having 2 to 3 carbon atoms; and n is preferably an integer of 1 to4 and is more preferably an integer of 2 to 4.

The alkylene glycol monoalkyl ether is exemplified, for example, byethylene glycol methyl ether, ethylene glycol ethyl ether, ethyleneglycol n-propyl ether, diethylene glycol methyl ether, diethylene glycolethyl ether, diethylene glycol n-propyl ether, diethylene glycol n-butylether, diethylene glycol n-hexyl ether, triethylene glycol methyl ether,triethylene glycol ethyl ether, triethylene glycol n-propyl ether,triethylene glycol n-butyl ether, tetraethylene glycol n-butyl ether,propylene glycol methyl ether, propylene glycol ethyl ether, propyleneglycol n-propyl ether, propylene glycol n-butyl ether, dipropyleneglycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycoln-propyl ether, dipropylene glycol n-butyl ether, tripropylene glycolmethyl ether, tripropylene glycol ethyl ether, tripropylene glycoln-propyl ether, and tripropylene glycol n-butyl ether. Among them, it ispreferable to use dipropylene glycol n-propyl ether, triethylene glycoln-butyl ether, and tetraethylene glycol n-butyl ether. The penetrant mayinclude any penetrant other than the alkylene glycol monoalkyl ether,but is preferably made only of the alkylene glycol monoalkyl ether. Onetype (kind) of the penetrant as described above may be used singly, ortwo or more types (kinds) of the penetrants as described above may beused in combination.

The mechanism in which the water-based ink having the superiorre-dispersion property can be obtained by using the glycerol and thediethylene glycol in combination as the humectant and using the alkyleneglycol monoalkyl ether as the penetrant is assumed, for example, asfollows. That is, the glycerol has a high hydrophilic property and thediethylene glycol has a hydrophilic property lower than that of theglycerol (the diethylene glycol has a hydrophobic property higher thanthat of the glycerol). In constituents of the water-based ink such as asurfactant, there is (are) the constituent(s) in which the compatibilitywith respect to the glycerol is a lot different from the compatibilitywith respect to the diethylene glycol. In a case that the constituentsare used in combination, an insoluble component is extracted after thedrying of the water-based ink and the re-dispersion property of thewater-based ink is deteriorated in some cases depending on the mixingratio of the glycerol and the diethylene glycol. In view of this, byfurther using the alkylene glycol monoalkyl ether in a mixture system ofthe glycerol and the diethylene glycol in combination, the alkyleneglycol monoalkyl ether functions as a compatibility-providing agent tosuppress the extraction and to improve the re-dispersion property. Thismechanism is just an assumption and the present teaching is not limitedthereto.

The blending amount of the penetrant with respect to the entire amountof the water-based ink is, for example, more than 0% by weight and notmore than 20% by weight, preferably 0.1% by weight to 15% by weight,more preferably 0.5% by weight to 10% by weight, and further preferably1.5% by weight to 3% by weight. Especially, by making the blendingamount of the penetrant to be 1.5% by weight to 3% by weight,compatibilizing effect of the penetrant is further improved, and makingit possible to further stabilize a dispersion state of pigmentparticles.

A total blending amount of the self-dispersible pigment modified bycarboxylic acid group, the glycerol, the diethylene glycol, and thealkylene glycol monoalkyl ether with respect to the entire amount of thewater-based ink is preferably 10% by weight to 60% by weight, and ismore preferably 15% by weight to 50% by weight. In a case that the abovetotal blending amount is less than 10% by weight, the viscosity of inklowers and there are fears that landing accuracy is decreased andsatellite droplets occur. In a case that the above total blending amountexceeds 60% by weight, the viscosity of ink increases and there is afear that the jetting failure in which the ink is less likely to bedischarged from the nozzles occurs.

The water-based ink may further contain conventionally known additives,if necessary. The additive includes, for example, surfactants,pH-adjusting agents, viscosity-adjusting agents, surfacetension-adjusting agents, and fungicides. The viscosity-adjusting agentis exemplified, for example, by polyvinyl alcohol, cellulose, andwater-soluble resin.

As described above, the water-based ink may contain conventionally knownadditives, if necessary. The total blending amount of the carboxylicacid group-modified self-dispersible pigment, the glycerol, thediethylene glycol, the alkylene glycol monoalkyl ether, and water in thewater-based ink is preferably 90% by weight to 100% by weight, morepreferably 95% by weight to 100% by weight, and most preferably 98% byweight to 100% by weight. In a case that the above total blending amountis 90% by weight to 100% by weight, it is possible to further suppressthe viscosity increase of the ink after the drying and to furtherimprove the re-dispersion property.

The water-based ink can be prepared, for example, as follows. That is,the carboxylic acid group-modified self-dispersible pigment, water, theglycerol, the diethylene glycol, the alkylene glycol monoalkyl ether,and other additive component(s) as necessary are mixed uniformly inaccordance with any conventionally known method, and then undissolvedmatters are removed by a filter or the like.

The viscosity of the water-based ink (viscosity without evaporation) ispreferably 2 mPa·S to 10 mPa·S. By making the viscosity of thewater-based ink to be not less than 2 mPa·S, jetting control becomeseasier and a desired imaging quality can be obtained more easily. Bymaking the viscosity of the water-based ink to be not more than 10mPa·S, the jetting stability is further improved.

As described above, in the water-based ink of the present teaching, thecarboxylic acid group-modified self-dispersible pigment is selected asthe colorant, the glycerol and the diethylene glycol are used incombination at a predetermined blending ratio as the humectant, and thealkylene glycol monoalkyl ether is contained as the penetrant. Thus,viscosity increases after the short-term drying and the long-term dryingare suppressed and the re-dispersion property is superior.

Next, an explanation will be given about an ink cartridge of the presentteaching. The ink cartridge of the present teaching is an ink cartridgecontaining a water-based ink for inkjet recording, wherein thewater-based ink is the water-based ink for inkjet recording of thepresent teaching. For example, any conventionally known main body (body)of an ink cartridge can be used for the main body of the ink cartridgeof the present teaching.

Next, an explanation will be made about an ink-jet recording apparatusand an ink jet recording method of the present teaching.

The ink-jet recording apparatus of the present teaching is an ink-jetrecording apparatus including an ink accommodating section and an inkdischarging mechanism which discharges an ink accommodated in the inkaccommodating section, wherein the water-based ink for ink-jet recordingof the present teaching is accommodated in the ink accommodatingsection.

The ink jet recording method of the present teaching is an ink jetrecording method for performing recording by discharging a water-basedink on a recording medium in an ink jet system, wherein the water-basedink for ink jet recording of the present teaching is used as thewater-based ink.

The ink-jet recording method of the present teaching can be performed byusing, for example, the ink jet recording apparatus of the presentteaching. The recording includes, for example, printing of letters(text), printing of images, printing, etc.

FIG. 1 shows an exemplary construction of the ink-jet recordingapparatus of the present teaching. As shown in FIG. 1, an ink-jetrecording apparatus 1 includes, as main constitutive elements, four inkcartridges 2, an ink discharging mechanism (ink jet head) 3, a head unit4, a carriage 5, a driving unit 6, a platen roller 7, and a purge unit8.

Each of the four ink cartridges 2 includes one of the four colorwater-based inks of yellow, magenta, cyan, and black one by one. Forexample, the water-based black ink is the water-based ink for ink jetrecording of the present teaching. General water-based inks may be usedfor the water-based inks other than the water-based black ink. The inkjet head 3, which is installed on the head unit 4, performs recording ona recording medium P (for example, recording paper sheet). The four inkcartridges 2 and the head unit 4 are carried on the carriage 5. Thedriving unit 6 reciprocatively moves the carriage 5 in a lineardirection. For example, a conventionally known driving unit can be usedas the driving unit 6 (see, for example, Japanese Patent ApplicationLaid-open No. 2008-246821 corresponding to United States PatentApplication Publication No. US 2008/0241398). The platen roller 7extends in the reciprocating direction of the carriage 5, and the platenroller 7 is arranged to face or to be opposite to the ink jet head 3.

The purge unit 8 sucks any defective ink containing bubbles or the likeremaining at the inside of the ink jet head 3. For example, aconventionally known purge unit can be used as the purge unit 8 (see,for example, Japanese Patent Application Laid-open No. 2008-246821corresponding to United States Patent Application Publication No. US2008/0241398).

A wiper member 20 is arranged adjacently to the purge unit 8 at aportion of the purge unit 8 on a side of the platen roller 7. The wipermember 20 is formed to have a spatula-shaped form. The wiper member 20wipes a nozzle-formed surface of the ink jet head 3 in accordance withthe movement of the carriage 5. With reference to FIG. 1, a cap 18covers a plurality of nozzles of the ink jet head 3, which is returnedto the reset position when the recording is completed, in order toprevent the water-based inks from being dried.

In the ink-jet recording apparatus 1 of this embodiment, the four inkcartridges 2 are carried on one carriage 5 together with the head unit4. However, the present teaching is not limited to this. In the ink jetrecording apparatus described above, the respective four ink cartridges2 may be carried on any carriage distinctly from the head unit 4.Alternatively, the respective four ink cartridges 2 may be arranged andfixed in the ink-jet recording apparatus without being carried on thecarriage 5. In the modes as described above, for example, the respectivefour ink cartridges 2 are connected to the head unit 4 carried on thecarriage 5 by tubes or the like, and each of the water-based inks issupplied from one of the four ink cartridges 2 to the head unit 4.

The ink jet recording, which uses the ink jet recording apparatus 1, iscarried out, for example, as follows. At first, a recording paper sheetP is supplied from a paper-feeding cassette (not shown) provided in theink-jet recording apparatus 1 on a side portion or lower portionthereof. The recording paper sheet P is introduced between the ink-jethead 3 and the platen roller 7. A predetermined recording is performedon the introduced recording paper sheet P with the water-based ink(s)discharged from the ink jet head 3. In the water-based ink of thepresent teaching, the viscosity increases after the short-term dryingand the long-term drying are further suppressed compared withconventional water-based inks and the re-dispersion property issuperior. Thus, it is possible to discharge the water-based ink from theink jet head 3 stably. The recording paper sheet P for which therecording has been performed is discharged from the ink jet recordingapparatus 1. In FIG. 1, illustrations of the paper-feeding mechanism andpaper-discharging mechanism for the recording paper sheet P are omitted.

The apparatus shown in FIG. 1 adopts the serial type ink jet head.However, the present teaching is not limited to this. The ink-jetrecording apparatus may be an apparatus which adopts a line type ink jethead.

EXAMPLES

Next, Examples and Comparative Examples of the present teaching will beexplained. Note that the present teaching is not limited to and is notrestricted by the Examples and Comparative Examples which will bedescribed below.

Examples 1 to 10 and Comparative Examples 1 to 10

Components except for a self-dispersible carbon black, which wereincluded in the Water-based Ink Composition (TABLE 1), were mixeduniformly or homogeneously; and thus an ink solvent was obtained.Subsequently, the ink solvent was added to each of the self-dispersiblecarbon black water dispersions, followed by being mixed uniformly. Afterthat, the obtained mixtures were each filtrated through a celluloseacetate membrane filter (pore size 3.00 μm) produced by Toyo RoshiKaisha, Ltd., and thus the water-based inks for ink-jet recording ofExamples 1 to 10 and Comparative Examples 1 to 10 were obtained.

The water-based inks in Examples and Comparative Examples were used toperform (a) evaluation of rate of viscosity change after evaporation inlow shear area, (b) evaluation of rate of viscosity change afterevaporation in high shear area, (c) evaluation of water-based ink afterevaporation by microscopic observation, and (d) evaluation ofre-dispersion property in the following methods.

(a) Evaluation of Rate of Viscosity Change after Evaporation in LowShear Area

5 g of each of the water-based inks in Examples and Comparative Exampleswas poured into an open vial (opening size (diameter): 20.2 mm). Theopen vial was stored in a thermostatic chamber for 5 days at atemperature of 60 degrees Celsius and a relative humidity of 40%. Then,the viscosity of each of the water-based inks in the open vial after thestorage was measured by using a viscometer (produced by TA instruments,product name: AR-G2, cone-plate geometry (diameter: 40 mm, cone angle:1°) was used as geometry) under the conditions in which a shear velocitywas 10 sec⁻¹ and a measurement temperature was 25 degrees Celsius. Foreach of the water-based inks in Examples 1 to 10 and ComparativeExamples 1-5, 7, and 8, a relative value (rate of viscosity change) ofthe viscosity after the evaporation in the low shear area was calculatedon the assumption that the viscosity after the evaporation in the lowshear area of Comparative Example 6, in which the humectant was madeonly of the glycerol, was set as 1. Then, each of the relative valueswas evaluated in accordance with the following evaluation criteria.

<Evaluation Criteria for Evaluation of Rate of Viscosity Change afterEvaporation in Low Shear Area>

A+: Rate of viscosity change after evaporation in low shear area wasless than 0.5

A: Rate of viscosity change after evaporation in low shear area was notless than 0.5 and less than 0.7

B: Rate of viscosity change after evaporation in low shear area was notless than 0.7 and less than 1

C: Rate of viscosity change after evaporation in low shear area was notless than 1

(b) Evaluation of Rate of Viscosity Change after Evaporation in HighShear Area

The viscosity of each of the water-based inks in the open vial wasmeasured in the similar manner as the evaluation of the rate ofviscosity change after the evaporation in the low shear area, exceptthat the shear velocity of the viscometer was set to 100 sec⁻¹. For eachof the water-based inks in Examples 1 to 10 and Comparative Examples 2to 8, a relative value (rate of viscosity change) of the viscosity afterthe evaporation in the high shear area was calculated on the assumptionthat the viscosity after the evaporation in the high shear area ofComparative Example 1, in which the humectant was made only of thediethylene glycol, was set as 1. Then, each of the relative values wasevaluated in accordance with the following evaluation criteria.

<Evaluation Criteria for Evaluation of Rate of Viscosity Change afterEvaporation in High Shear Area>

A+: Rate of viscosity change after evaporation in high shear area wasless than 0.5

A: Rate of viscosity change after evaporation in high shear area was notless than 0.5 and less than 0.7

B: Rate of viscosity change after evaporation in high shear area was notless than 0.7 and less than 1

C: Rate of viscosity change after evaporation in high shear area was notless than 1

(C) Evaluation of Water-Based Ink after Evaporation by MicroscopicObservation

Each of the water-based inks in the open vial after the storage used inthe evaluation of the rate of viscosity change after the evaporation inthe low shear area was observed by using a X200-magnification opticalmicroscope. Then, each of the water-based inks was evaluated inaccordance with the following evaluation criteria.

<Evaluation Criteria for Evaluation of Water-Based Ink after Evaporationby Microscopic Observation>

G: No aggregation was observed

NG: Aggregation was observed

(d) Evaluation for Re-Dispersion Property

The water-based inks of Examples and Comparative Examples were drippedeach in amount of 12 μL onto glass slides, respectively. Subsequently,the glass slides were stored for duration of one day under anenvironment of temperature: 60 degrees Celsius and relative humidity:40%, and thus the water-based inks were evaporated and dried. 1 mL ofpure or purified water was dripped onto each of solid matters after thestorage. With respect to the evaluation samples prepared in such amanner, presence or absence of residue was observed visually and byusing a X200-magnification optical microscope. The re-dispersionproperty was evaluated in accordance with the following evaluationcriteria.

<Evaluation Criteria for Re-Dispersion Property>

A+: Solid matter was re-dispersed uniformly (dissolved and dispersed inpure water) upon dripping of pure water, and any residue was notobserved visually and microscopically.

A: Solid matter was re-dispersed uniformly upon dripping of pure water,and any residue was not observed visually but some residue was observedmicroscopically.

B: Although solid matter was re-dispersed uniformly upon dripping ofpure water, some residue was observed visually and microscopically.

Ink compositions and evaluation/measurement results of the water-basedinks of Examples and Comparative Examples are shown in Table 1.

In TABLE 1:

*1: Self-dispersible carbon black modified by carboxylic acid group,manufactured by Cabot Specialty Chemicals; carbon black concentration:15% by weight, number in parenthesis indicates pigment solid contentamount

*2: Self-dispersible carbon black modified by sulfonic acid group,manufactured by Cabot Specialty Chemicals; carbon black concentration:15% by weight, number in parenthesis indicates pigment solid contentamount

*3: Acetylene diol ethylene oxide (10 mol) adduct, produced by NissinChemical Industry Co., Ltd

*4: Unmeasurable

TABLE 1 EXAMPLES 1 2 3 4 5 6 7 Water-based Ink CAB-O-JET (trade name)300 (*1) 26.7 26.7 26.7 26.7 26.7 26.7 26.7 Composition (4.0) (4.0)(4.0) (4.0) (4.0) (4.0) (4.0) (% by weight) CAB-O-JET (trade name) 200(*2) — — — — — — — Glycerol (Gly) 2.00 4.00 5.00 6.00 7.00 19.00 5.00Diethylene glycol (DEG) 23.00 21.00 20.00 19.00 18.00 6.00 20.00Dipropylene glycol-n-propylether 1.20 1.50 1.00 2.00 3.00 2.50 —Triethylene glycol-n-butyl ether — — — — — — 2.00 Tetraethyleneglycol-n-butyl ether — — — — — — — Polyallylamine (molecular weight3000) — — — — — — — 2-n-butyl-2-ethyl-1,3-propanediol — — — — — — —2-ethyl-1,3-hexanediol — — — — — — — Olfine (trade name) E1010 (*3) 0.200.20 0.20 0.20 0.20 0.20 0.20 Water balance balance balance balancebalance balance balance DEG/(Gly + DEG) 0.92 0.84 0.80 0.76 0.72 0.240.80 Evaluation/ Viscosity after evaporation in low shear 260 120 102 99110 172 122 Measurement area (mPa · S) Viscosity after evaporation inhigh shear 123 96 74 74 88 130 68 area (mPa · S) Rate of viscositychange after 0.90 0.42 0.35 0.34 0.38 0.60 0.42 evaporation in low sheararea B A+ A+ A+ A+ A A+ (obtained with reference to Comparative Example6) Rate of viscosity change after 0.82 0.64 0.49 0.49 0.58 0.86 0.45evaporation in high shear area B A A+ A+ A B A+ (obtained with referenceto Comparative Example 1) Observation of water-based ink after G G G G GG G evaporation by using microscope Re-dispersion property A A+ A A+ A+A+ A+ EXAMPLES COMPARATIVE EXAMPLES 8 9 10 1 2 3 4 Water-based InkCAB-O-JET (trade name) 300 (*1) 26.7 26.7 26.7 26.7 26.7 26.7 26.7Composition (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (4.0) (% by weight)CAB-O-JET (trade name) 200 (*2) — — — — — — — Glycerol (Gly) 5.00 15.0015.00 — 1.00 2.00 20.00 Diethylene glycol (DEG) 20.00 10.00 10.00 25.0024.00 23.00 5.00 Dipropylene glycol-n-propylether — — — 1.50 2.00 — 3.00Triethylene glycol-n-butyl ether 1.50 — — — — — — Tetraethyleneglycol-n-butyl ether — 2.00 3.00 — — — — Polyallylamine (molecularweight 3000) — — — — — — — 2-n-butyl-2-ethyl-1,3-propanediol — — — — — —— 2-ethyl-1,3-hexanediol — — — — — — — Olfine (trade name) E1010 (*3)0.20 0.20 0.20 0.20 0.20 0.20 0.20 Water balance balance balance balancebalance balance balance DEG/(Gly + DEG) 0.80 0.40 0.40 1.00 0.96 0.920.20 Evaluation/ Viscosity after evaporation in low shear 132 153 163612 450 279 223 Measurement area (mPa · S) Viscosity after evaporationin high shear 70 115 120 151 136 115 193 area (mPa · S) Rate ofviscosity change after 0.46 0.53 0.57 2.13 1.56 0.97 0.77 evaporation inlow shear area A+ A A C C B B (obtained with reference to ComparativeExample 6) Rate of viscosity change after 0.47 0.76 0.80 ref 0.90 0.761.28 evaporation in high shear area A+ B B — B B C (obtained withreference to Comparative Example 1) Observation of water-based ink afterG G G G G G G evaporation by using microscope Re-dispersion property A+A+ A+ — A B A+ COMPARATIVE EXAMPLES 5 6 7 8 9 10 Water-based InkCAB-O-JET (trade name) 300 (*1) 26.7 26.7 — — 26.7 26.7 Composition(4.0) (4.0) (4.0) (4.0) (% by weight) CAB-O-JET (trade name) 200 (*2) —— 26.7 26.7 — — (4.0) (4.0) Glycerol (Gly) 24.00 25.00 5.00 25.00 7.005.00 Diethylene glycol (DEG) 1.00 — 20.00 — 23.00 15.00 Dipropyleneglycol-n-propylether — 3.50 — 2.00 — — Triethylene glycol-n-butyl ether— — — — — — Tetraethylene glycol-n-butyl ether — — — — — —Polyallylamine (molecular weight 3000) — — — — — 1.002-n-butyl-2-ethyl-1,3-propanediol — — — — 3.00 — 2-ethyl-1,3-hexanediol— — — — — 2.00 Olfine (trade name) E1010 (*3) 0.20 0.20 0.20 0.20 0.200.20 Water balance balance balance balance balance balance DEG/(Gly +DEG) 0.04 0 0.80 0 0.77 0.75 Evaluation/ Viscosity after evaporation inlow shear 276 288 1760 940 — (*4) Measurement area (mPa · S) Viscosityafter evaporation in high shear 243 254 856 321 — (*4) area (mPa · S)Rate of viscosity change after 0.96 ref 6.11 3.26 — — evaporation in lowshear area B — C C — — (obtained with reference to Comparative Example6) Rate of viscosity change after 1.61 1.69 5.67 2.13 — — evaporation inhigh shear area C C C C — — (obtained with reference to ComparativeExample 1) Observation of water-based ink after G G — — NG — evaporationby using microscope Re-dispersion property B A — — A —

As shown in TABLE 1, for each of the water-based inks in Examples 1 to10, the viscosity after the evaporation in the low shear area and theviscosity after the evaporation in the high shear area were lower thanthose of the water-based inks in Comparative Examples 1 and 6 asreferences. Further, in each of the water-based inks of Examples 1 to10, both the rate of viscosity change after the evaporation in the lowshear area and the rate of viscosity change after the evaporation in thehigh shear area were less than 1, and thus viscosity increases after theshort-term drying and the long-term drying could be suppressed.Furthermore, the result of the evaluation of the re-dispersion propertywas also superior in each of the water-based inks of Examples 1 to 10.Especially, for each of the water-based inks of Examples 3, 4, 7, and 8in which the glycerol and the diethylene glycol were blended to satisfythe condition (ii), the rate of viscosity change after the evaporationin the low shear area and the rate of viscosity change after theevaporation in the high shear area were less than 0.5 and they wereremarkably superior. In a case that the rate of viscosity change afterthe evaporation in the low shear area and the rate of viscosity changeafter the evaporation in the high shear area were less than 0.5,clogging of nozzles occurred when the water-based ink was discharged bythe ink jet head of the ink jet recording apparatus was suppressedespecially suitably and the jetting performance was further improved.For each of the water-based inks of Examples 2, and 4 to 10 in which theblending amount of the alkylene glycol monoalkyl ether was 1.5% byweight to 3% by weight, the result of the evaluation of there-dispersion property was especially superior.

On the other hand, in each of the water-based inks of ComparativeExamples 1, 2, and 4 to 6 in which the blending ratio of the glyceroland the diethylene glycol did not meet the condition (i), any of therate of viscosity change after the evaporation in the low shear area andthe rate of viscosity change after the evaporation in the high sheararea was not less than 1 and the viscosity increase after the dryingcould not be suppressed. Further, in the water-based ink of ComparativeExample 3 in which the alkylene glycol monoalkyl ether was not blended,the result of the evaluation of the re-dispersion property was inferior.In each of the water-based inks of Comparative Examples 7 and 8 in whichthe sulfonic acid group-modified self-dispersible pigment was usedinstead of the carboxylic acid group-modified self-dispersible pigment,both the rate of viscosity change after the evaporation in the low sheararea and the rate of viscosity change after the evaporation in the highshear area exceeded 1 substantially. In the water-based ink ofComparative Example 9 in which 2-n-butyl-2-ethyl-1,3-propanediol wasblended instead of the alkylene glycol monoalkyl ether, the result ofthe evaluation of the water-based ink after the evaporation by themicroscopic observation was inferior. In the water-based ink ofComparative Example 10 in which polyallyamine (molecular weight 3000)and 2-ethyl-1,3-hexanediol were used in combination instead of thealkylene glycol monoalkyl ether, the viscosity after the evaporation inthe low shear area and the viscosity after the evaporation in the highshear area were too high to measure the viscosity thereof.

As described above, in the water-based ink of the preset teaching,viscosity increases after the short-term drying and the long-term dryingare suppressed and the re-dispersion property is superior. The way ofuse of the water-based ink of the present teaching is not specificallylimited, and the water-based ink is widely applicable to various typesof ink jet recording.

What is claimed is:
 1. A water-based ink for ink jet recording,comprising: a self-dispersible pigment modified by carboxylic acidgroup; glycerol; diethylene glycol; alkylene glycol monoalkyl ether; andwater, wherein the glycerol and the diethylene glycol satisfy thefollowing condition (i):0.24≦DEG/(Gly+DEG)≦0.92  (i) in the condition (i), Gly represents anamount of the glycerol in the water-based ink (% by weight); and DEGrepresents an amount of the diethylene glycol in the water-based ink (%by weight).
 2. The water-based ink for ink jet recording according toclaim 1, wherein the glycerol and the diethylene glycol satisfy thefollowing condition (ii):0.76≦DEG/(Gly+DEG)≦0.80  (ii) in the condition (ii), Gly represents theamount of the glycerol in the water-based ink (% by weight); and DEGrepresents the amount of the diethylene glycol in the water-based ink (%by weight).
 3. The water-based ink for ink jet recording according toclaim 1, wherein the alkylene glycol monoalkyl ether is contained in thewater-based ink in an amount of 1.5% by weight to 3% by weight.
 4. Thewater-based ink for ink jet recording according to claim 1, wherein thewater-based ink does not contain a dye.
 5. The water-based ink for inkjet recording according to claim 1, wherein the water-based ink containsonly the self-dispersible pigment modified by carboxylic acid group as acolorant.
 6. The water-based ink for ink jet recording according toclaim 1, wherein the alkylene glycol monoalkyl ether is represented bythe following general formula (1):R¹O—(R²O)_(n)—H  (1) in the general formula (1), R¹ is an unsubstitutedstraight-chain alkyl group having 1 to 6 carbon atoms; R² is anunsubstituted straight-chain alkylene group having 2 to 3 carbon atoms;and n is an integer of 1 to
 4. 7. The water-based ink for ink jetrecording according to claim 1, wherein the alkylene glycol monoalkylether is at least one selected from the group consisting of dipropyleneglycol n-propyl ether, triethylene glycol n-butyl ether, andtetraethylene glycol n-butyl ether.
 8. The water-based ink for ink jetrecording according to claim 1, wherein a total amount of theself-dispersible pigment modified by carboxylic acid group, theglycerol, the diethylene glycol, the alkylene glycol monoalkyl ether,and water in the water-based ink is 90% by weight to 100% by weight. 9.The water-based ink for ink jet recording according to claim 1, whereina total amount of the glycerol and the diethylene glycol in thewater-based ink is 10% by weight to 60% by weight.
 10. The water-basedink for ink jet recording according to claim 1, wherein the glycerol iscontained in the water-based ink in an amount of 1% by weight to 45% byweight.
 11. The water-based ink for ink jet recording according to claim1, wherein the diethylene glycol is contained in the water-based ink inan amount of 2% by weight to 55% by weight.
 12. An ink cartridgecontaining the water-based ink for ink jet recording as defined inclaim
 1. 13. An ink jet recording apparatus comprising: an inkaccommodating section in which the water-based ink for ink jet recordingas defined in claim 1 is accommodated; and an ink discharge mechanismwhich is configured to discharge the water-based ink for ink jetrecording accommodated in the ink accommodating section.
 14. An ink jetrecording method comprising: preparing a recording medium; anddischarging the water-based ink for ink-jet recording as defined inclaim 1 onto the recording medium.